1. Field of the Invention
The present invention relates generally to flexible substrates and, more specifically, to tape-based substrates that include copper layers. In particular, the present invention relates to tape-based substrates with mold gates that are configured so as to require only a single copper layer.
2. Background of Related Art
Numerous semiconductor packaging methodologies have found widespread use. Among those that have been commonly used is the so-called “board-on-chip” arrangement of a substrate relative to a semiconductor die. As its name implies, a substrate, or “board,” which provides a connection pattern of input and output elements (e.g., contacts, leads, or other electrodes) is positioned on a semiconductor die. Typically, the substrate is positioned on the bond pad (i.e., input/output electrode) bearing surface, or “active” surface, of the semiconductor die.
In order to provide the desired connection pattern, a substrate typically includes a planar dielectric member, electrical contacts on the die-facing side of the substrate, conductive traces that extend laterally along the dielectric planar member, and redistributed contact pads, or “terminals,” that are exposed at the opposite surface of the substrate. A substrate may also include conductive vias that extend through at least a portion of the thickness of the substrate to connect contacts to corresponding conductive traces.
In addition, to facilitate the formation of a molded protective structure, or “package,” around the substrate-semiconductor die assembly, the substrate may also include a mold gate. A mold gate is a feature on the substrate which is configured to communicate with a mold runner through which liquid packaging material is introduced into a mold cavity and to direct the liquid packaging material to desired locations in a desired fashion.
Conventionally, when the substrate of a semiconductor device assembly is a so-called “two-layer flex” or “adhesiveless flex” tape-based substrate, or, more simply, a “tape substrate” 1, it will include a flexible dielectric film 2 (e.g., polyimide) and a layer of conductive traces 6, which are typically etched from a conductive (e.g., copper) film that was laminated to the polymeric film, that are carried upon a surface of the flexible dielectric film 2, as shown in FIG. 1A. At least one side, or surface 3, of tape substrate 1 carries conductive traces 6. Packaging, or encapsulating, material is typically introduced over surfaces of the tape substrate 1 and a semiconductor die thereon from the opposite side, or surface 4, of the tape substrate 1. As a result, the mold gate 5 is positioned on the opposite side, or surface 4, of the tape substrate 1 from that which carries the conductive traces 6.
Alternatively, as shown in FIG. 1B, when the substrate of a semiconductor device assembly is a so-called “three-layer flex” or “adhesive flex” tape substrate 1′, it will include a flexible dielectric film 2, adhesive material 7 on at least one surface 3 of tape substrate 1′, and conductive traces 6 that are secured to surface 3 by way of adhesive material 7.
As the dielectric film 2 is flexible, the mold gates 5 of tape substrates 1, 1′ are typically formed by laminating an additional material layer to the surface 4 of the tape substrate 1, 1′ which is opposite from the conductive trace-bearing surface 3 of the tape substrate 1, 1′. This additional material layer may be used to form the mold gate 5 itself, or to support a mold gate 5 which has been formed in the flexible dielectric film 2. Of course, the requirement that two material layers be laminated onto a flexible dielectric film 2 and, thus, separately patterned, undesirably increases the cost of fabricating the tape substrate 1, 1′. Moreover, the use of an additional material layer to form a mold gate 5 may undesirably increase the thickness of the tape substrate 1, 1′, which is counter to the trend toward semiconductor device packages of ever-decreasing dimensions.
Further, conventional tape-automated bonding (TAB) substrates, which include flexible dielectric films by which conductive traces and contacts, or terminals, are carried, are typically formed by mechanically punching the flexible dielectric film, laminating or adhesively securing a conductive film to a single surface of the flexible dielectric film, then patterning the conductive film to form conductive traces, contacts, and other conductive features. Because conventional tape substrates require that two conductive films be positioned on opposite surfaces of the flexible dielectric films thereof, many TAB substrate manufacturers are unable or unwilling to fabricate tape substrates.
Accordingly, there is a need for a mold gate configuration and mold gate fabrication methods which do not contribute to the thickness of a tape substrate of which the mold gate is a part or to the cost of fabricating the tape substrate.